Bag making machine



May 5,1959 JCD NeELo 7 BAG MAKING MACHINE Filed Sept. 30, 1954 4 Sheets-Sheet 1' F0 I9 I18 l 9b mmvroa.

k JOSEPH DANsELo Fig, 2. Qmmmm a sownav.

ATTORNEYS May 5, 1959 J. D'ANGELO BAG MAKING MACHINE 4 Sheets-Sheet 2 Filed Sept. 30, 1954 IN VEN TOR.

D'ANGELQ.

JOSEPH ATTORNEYS.

May 5,1959 7 J. D'ANGELO 2,384,988

BAG MAKING MACHINE Filed Sept. 30, 1954 4 Sheets-Sheet a INVENTOR.

J OSEPH' YDANGELO ,momim$&\\onk. ATTORNEYS y 1959 J. D'ANGELO 2,884,988

BAG MAKING MACHINE Filed Sept. 30, 1954 4 Sheets-Sheet 4 EXHAUST INVENTOR.

JOSEPH D'ANsELo BY AT RNE s Unite States BAG MAKING MACHINE Joseph DAngelo, Flushing, N.Y., assignor to Roto llag Machine Corporation, New York, N.Y., a corporation of New York Application September 30, 1954, Serial No. 459,477

9 Claims. (Cl. 154-42) This invention relates to improvements in pouch and bag making machines, and particularly to an improved machine for making plastic bags, pouches and similar containers of heat-scalable material from a continuously moving web.

Bags, pouches and similar containers as contemplated herein comprise front and back panels that are joined on three sides, with the remaining side left open for filling purposes. Containers of this type wherein one of the panels extends somewhat beyond the other at the open end of the container to form a closure flap are referred to herein as pouches, Whereas the term bag is used in its generic sense to include pouches as well as those containers having coextensive panels.

It is among the objects of the present invention to provide an improved bag-making machine in which juxtaposed layers of heat-scalable material are passed through the machine at a uniform high rate of speed and sealed together at spaced intervals to form the side edges of the individual containers, which can then be separated from each other at the points of sealage, all without interfering with the movement of material through the machine. Another object of the invention is the provision of a novel mechanism for making regularly spaced heat seals in a rapidly moving, continuous web of heat-scalable material by means of elements that are moved back and forth along the path of travel of the material to perform heat-sealing operations thereon, all at high rates of speed. A further object of the invention is the provision of means for forming heat seals across relatively wide surface areas of juxtaposed layers of heat-scalable material without appreciable shrinkage or wrinkling of the material.

In accordance with a preferred embodiment of the invention, the foregoing and other objects and advantages are attained in a machine wherein a continuous web of heat scalable material is drawn from a supply roller at a high rate of speed and passed over a folding table which shapes the material to form two double-layered strips connected by a relatively narrow central web. The folded material then passes through a heat sealing mechanism which includes clamping elements that are movableback and forth parfllel to the path of travel of the material by means of magnetic-clutch-driven winches and associated cables. During their travel in the direction of movement of the material, the clamping elements are brought together with the moving material layers therebetween, and heat is applied to the clamped layers to seal them together. Synchronization of the forward drive and the clamping action is simplified by utilizing the time delay introduced by a pneumatic actuator in bringing the clamping elements together. Because of the instantaneous response of the magnetic clutches, the clamping elements will be moving forward at the same speed as the material before the slower-acting pneumatic actuator brings the clamping elements together, thereby avoiding any interference with the moving material and without involving problems of synchronization between the fore aft drive and the clamping actuator. Upon completion 2,884,988 Patented May 5, 1959 of the heat sealing operation, the clamping elements are disengaged and returned to their starting point at a high rate of speed, in readiness for the next heat sealing pass. In order to prevent rebound of the clamping elements when they reach the end of their return travel, the return drive clutch is left partially'engaged to continue applying a (reduced) return force to the clamp assembly, thereby overcoming the tendency to rebound. To prevent shrinkage or wrinkling of the material duringthe sealing opera tion, one of the clamping elements preferably has a pattern of raised lines on its material-engaging surface which reduces the actual contact area of the clamping elements without reducing the total extent (width) of the seal. Upon leaving the heat sealer, the moving material is passed through a rotary knife or other cutting mechanism to separate the pairs of pouches or bags.

A more complete understanding of the invention, and of further objects and features thereof, can be had by reference to the following description of an illustrative embodiment thereof, whenconsidered in connection with the accompanying drawings, wherein:

Figure 1 is a schematic diagram showing the organization of the parts in an apparatus embodying the present invention;

Figure 2 is a sectionview of the folding table with the material folded therearound, taken on a line corresponding to the line 2-2 in Figure. 1;

Figure 3 is a plan view of the material after it has been sealed in accordance with the invention;

Figure 4 is a perspective view of the perforator-slitter and the feed roll portion of-the apparatus of Figure 1;

Figure 5 is a perspective view' of the heat sealer in the apparatus of Figure 1;

Figure 6 is a section view of the heat sealer, taken on the line 6-6. of Figure 5;v and Figure 7 is a schematic diagram of the electric circuit for the apparatus of Figure 1.

As shown diagrammatically in Figure l of the drawings, the path of travel of a continuous web of plastic material through a machine embodying the present invention may extend from a supply roller 10 over a series of idler-guide rollers 12, 14, and 16 to a folding table 18. At the table-18 (see. also Figure 2)., edge portions 1% and 19b of width approximately one-fourth that of the original web 8 may be folded up under the table, so that as the material leaves the table these edge portions 19a and 1% will underlie the central portion 8a of the Web. Each of these edge portions cooperates with the corresponding overlying section of the central portion 8a to constitute the front and back panels of two continuous series of pouches or bags. Stated in a different Way, the material leaving the folding table 18 comprises two adjacent pairs of juxtaposed layers 8a and 19a, and 3a and 19b, joined by a narrow center strip.

In the example illustrated in Figure 2, it can bev seen that the edges of the two underlying sections 19a and 19b do not quite come to the center of the overlying portion 8a. In this case, the containers delivered from the machine will comprise pouches as previously defined. If, however, the edges of the sections 1911 and 19b were made to meet at the centerline of the web 8, the finished containers would constitute bags Without an extending flap.

As the material 8 leaves the table 18, it may be slit lengthwise along the centerline 23 by a knife 20. .In this. case, the completed bags will come from the machine as. Alternatively, if preferred,

pairs then can be separated readily as needed by tearing along the centerline perforation. As is explained more fully hereinafter, the knife 20 and perforator 22 are movable into and out of the material path selectively to allow either to be used as desired.

The moving material 8 next is drawn between a pair of feed rollers 26 and 28 which may constitute the first positively driven rollers in the path of travel, as indicated by the broken line extending from the drive motor 32 to the lower roller 28. Leaving the rollers 26 and 28, the material passes between the upper and lower clamping elements 34 and 36 of a heat sealing mechanism 40.

The clamping elements 34 and 36 are movable as a unit back and forth parallel to a portion of the path of the web by cables 42 and 44 connected to winches and 48. Also, the clamping elements 34 and 36 are arranged to be moved into and out of engagement with each other by an actuator (not shown in Figure 1) during the fore and aft movement thereof. When the clamps 34 and 36 are engaged, heat is applied to the portions of the material held therebetween to form a transverse heat seal 50, as indicated in Figure 3. The heating means (not shown in Figure 1) may comprise heating elements mounted in the clamping elements, or may comprise induction heating apparatus which will heat the material without heating the clamping elements. In either case, as the material leaves the sealer 40, the overlying layers thereof will be sealed laterally, as shown in Figure 3, along regularly spaced lines 50. In the example shown in Figure 3, it is assumed that the material was folded to leave a connecting strip of appreciable width between the adjacent pairs of layers of material, as in Figure 2, and that the perforator 22 was used to perforate along the centerline 23. It is seen that there are thus formed two continuous series of pouches, there being one pouch defined on each side of the centerline by each adjacent pair of seals 50. Of course, had the material been folded in such fashion as to bring the outside edges thereof nearly together at the centerline 23, two similarly continuous series of bags would have been formed. Also, had the knife 20 been used, the two series of containers would be completely disconnected from each other along the centerline 23.

The material leaving the sealer 40 passes between a second set of feed rollers 52 and 54, and then between the fixed and rotating blades 56 and 58 of a rotary cutter. Here the material is cut along the center of each of the lateral seal lines 50 to separate the pouches (or pairs of pouches), which then are carried out of the machine on a moving delivery bed comprising endless spring-cords 64 which pass around a pair of rollers 66 and 68 spaced along the path of travel.

To insure proper coordination between the various operations in the machine, the rollers 28, 54, and 68 and the winches 46 and 48 all are linked by gears, sprockets or the like (not shown) to be driven in unison by the motor 32, as indicated by the various broken lines conmeeting the designated parts. Also, the winch and clamp actuators are synchronized with the rotation of the cutter blade 58 by a switch-actuating cam 70 which functions in an electric circuit described hereinafter to insure that the cutter operation will be properly related to the placement of the seals 50.

It will be understood that a number of the features of the present invention are not limited to an apparatus in which the material is folded to form the bag or pouch panels in the precise manner shown from a single strip of material, as the heat sealer mechanism per se is applicable generally where spaced seals are required in a continuously and uniformly moving web of material or juxtaposed layers thereof.

As the details of mounting of the supply roll 10, as well as the precise configuration of the folding table 18, are not essential to an understanding of the invention, and may take a number of different forms, it is deemed unnecessary to include such details beyond the diagrammatic indication thereof given in Figures 1 through 3. Accordingly, consideration will now be given to the parts immediately preceding the heat sealer as shown in Figure 4.

In Figure 4, which shows the slitter-perforator assembly and the feed rollers 26 and 28, it can be seen that the backing roller 24 for the perforator wheel 22 is journalled above the path of material travel in a supporting bracket 72 which is mounted on a rod 74 extending laterally of the material path between side frame members 76. Below the material path, the perforating wheel and slitting knife assembly is mounted on brackets 78 fixed to a support plate 80 extending between the frame members 76.

The slitting knife and perforator wheel 22 are mounted at opposite ends of a rocker arm 82 which extends generally parallel to the material path and is pivotally mounted on a shaft 84 extending between the brackets 78. The shaft 84 is provided with a locking knob 86 threaded onto one end of the shaft and adapted to be turned up against the adjacent support bracket 78 to clamp the arm 82 either with the perforator wheel 22 engaging the backing roller 24 or with the perforator end of the arm 82 tilted downwardly away from the backing roller to bring the knife 20 up into the path of travel of the material, as desired.

Immediately beyond the slitter-perforator assembly, the first set of drive rollers 26 and 28 is joumalled in bearings 88 and 90 in the side members 76, with the lower roller 28 being provided with a drive gear 88. The upper roller bearings 90 are mounted in vertically slidable blocks 92. Pins 94 extending upwardly from the blocks 92 pass through cam plates 96 which extend over the blocks 92. At their upper ends, the pins 94 are swiveled to manually operable cams 98 in a toggle mechanism by means of which the pins can be raised against the action of springs 100 that normally urge the pins downwardly. The cams 98 are linked by a connecting rod 102 to be operated in unison by a handle 104. Thus, the rollers 26 and 28 can be separated by swinging up the handles 104, thus tilting the cams downwardly to permit feeding the material between the rollers when the machine is first put in operation. When the cams are raised to release the pins 94, the springs 100 will push the pins downwardly, thereby forcing the upper roller 26 tightly against its companion 28, with the material held therebetween.

It will be understood that the feed rollers 52 and 54 at the other end of the heat sealer 40 in Figure 1 are constructed and arranged in substantially the same manner as the rollers 26 and 28 just described, so that the foregoing description is considered to apply to both sets of rollers. Of course, as previously mentioned in connection with the discussion of Figure 1, the two sets of rollers 26 and 28, and 54 and 56 are suitably linked to be driven at the same rate of speed, thereby to insure uniform movement of the material through the heat sealer 40 which is shown in Figures 5 and 6.

As shown in Figures 5 and 6, the heat sealer comprises a main supporting bar 106 slidably mounted on a pair of rails 108 which extend parallel to the path of material travel on opposite sides thereof. The support bar 106 carries a first clamping element 36 on the upper side thereof, and, in the present embodiment of the invention, this clamping element 36 has a longitudinal cavity. contining an electrical heater cartridge 110 which is supplied with current by a circuit described hereinafter.

In accordance with one feature of the invention, the material-engaging upper surface of the lower clamping element 36 has a reverse knurl or surface pattern of raised lines 112, of diamond or other configuration. This is so that the contacting surfaces of the clamping elements 34 and 36 will meet across a relatively broad area and,

rially reduced without appreciably etfectingthestrength Also, the power required'for. the sealing:

of the seal. heat can be reduced to some extent.

The support bar 106 is provided at its opposite ends with vertical holes. through which. extend; a pair of rods 114 that are slidable vertically with-respect to the bar 106. A second support bar 116 that extends betweenthe two rods 114 is similarly slidable vertically onthe' rods 114, and carries on its underside a second clamping element 34. This clamping-element. also has an electrical heating cartridge 110 mounted inv a longitudinal cavity therein.

The upper support bar 116 is held resiliently between.

the lower support 106 and the upper ends of therods 114 by a first pair of springs 118 which extend between the supports 106 and 116, and a second pair of springs 120 which extend from the upper support 116 to adjusting nuts 122at the upper ends of the rods 114. Thus, upon vertical movement of the guide rods 114, the upper clamping element 34 can be moved downwardly into engagement with the lower clamp 36. The springs 118,.

120 make it unnecessary to adjustthe vertical movement of the rods 114 precisely, while insuring that the elements 34, 36 will come together under substantially constant pressure.

The means for reciprocating the rods 1 14 torraise'and lower the upper support bar 116 and its-associatedclamp 36, as shown in Figure 6,- comprises. a pneumaticactuator carried by a spacer bar 124which extends between.

the lower ends of the rods 114. The pneumatic actuator includes a cylinder 126 depending from the underside of the spacer 124 and houses a piston. 128 which: is

adapted to be raised by admission of compressed air to the underside of the piston through a valve 130. An

actuating pin 131 (please see Figure.v 6) extends from the upper side of the piston and makes contact with the underside of the mainsupport bar 106. Thus, as compressed air enters the cylinder, the movement of the piston and actuating pin will force the cylinder, the spacer 124 and the rods 114'to move downwardly, carrying with them the upper support 116 and the clamping element 34; at the same time partially compressing the springs 118 and 120.

At the end of the desired heat-sealing interval, the air exhausted from the cylinder 126 through the valve 130, whereupon the springs 118 and 120 will force the assembly 114, 116', and 124 to move upwardly, carrying with it the cylinder 126 and forcing the piston back down. The valve 130 is controlled by a solenoid actuator, as described hereinafter.

In addition to the reciprocating motion of the clamp 36, it is necessary for the clamp assembly to move with the material during the sealing process inorder not to interrupt the flow of material through the machine. It is for this reason, of course, that the main support 106:

is mounted on the rails 108 and is slidable therealong.

The mechanism for imparting fore-and-aft motion to the heat sealer (Figure 5) includes two fiexible' drive elements 132 and 133 formed of hardened steel cables covered with nylon and which are secured to opposite sides of the main support bar 106 andextendin opposite directions (parallel to the path of material travel) to guide pulleys 134 at opposite ends. of the heat sealer. The cables 132 and 1-33 pass over: the:pulle.y;s. 134 and terminate respectively at winches 46 and 48 which are.

mounted on shafts 136 and 137 below the. clamp assembly.

It has been The-winch shafts 136 and 137'are keyed to. the driven sections-138mm 1390f a pair of magnetic clutches=140 and 142; In turn, the driving sections 144 and 145 of the clutches. are fixed to drive shafts 146 and 147 which.

are coupled by gears 148 and 149 to rotate in unison in opposite directions in response to driving force applied to the shafti147 through a gear or sprocket 150.

The drivingand drivenportions of the clutches 140 and142 are adapted to be-engaged magnetically in the, customary fashion by passing electric current through magnetizing coils'(not shown in Figure 5) in the driving sections of the clutches. driven at thesame speed by the gears 148 and 149, the winch shafts'136 and'137 will rotate at the same speed; However, at the end of each heat sealing pass, it is necessary to return the sealing mechanism to its starting. position. rapidly in order thatthe material can be moved.

through the. mechanism at high speed and yet have reasonably close' spacing between the heat seals. Accordingly, the return-drive winch 46 is made somewhatlarger in diameter. than the forward-drive'winch 48 in order to have'a relatively rapid return rate; a ratio of 4 to 1 between the circumferences of the return and forward drive winches being typical.

To' absorb the shock of the return travel of the sealer. mechanism, resilient bumpers 152 are mounted on the rear face of the main support bar 106 to engage stops 154. A switch actuator 156 also projects from the rear:

face of the main support to operate a switch 158 (Figure. 7). The switch 158 is connected in a circuit which supplies a small amountof energizing current to the return:

drive clutch 142 whenever the sealing mechanism en-.

gages the stops 154. The purpose of this is to prevent the heat sealer from rebounding when it strikes the. stops..- 154 and prior to actuation of the forwarddrive clutch. 140. The electrical circuit for the apparatus is shown.

schematically in Figure 7, and will now be described.

The circuit of Figure 7 includes input leads 160 through which power is supplied from a conventional alternating: current source (not shown) for actuating the drive: motors, energizing the clutches and operating the heater.

elements. Beyond a main power switch 162, the compressor and main drive motors 164 and 32 are connected in parallel across the input lines 160 through separate manual switches 166 and 168. The circuit section for controlling the actuation of the clutches and of the air. valve solenoid is in-parallel with the motor 32, and includes a relay having an actuating winding 172 which is connected between the main motor switch 168 and the actuator 70 which, as shown in Figure 1, is arranged torotate in synchronism with the rotation of the rotary cutter 58'. In practice, the cam 70 may comprise separate cam elements on a single shaft for greater flexibility in timing the switch operation.

The fixed-contact 184 of the normally open switch 182" is connected to one of the supply lines 160, and is connected also to the movable contact 186 of a normallyopen section 170a of the relay 170. The fixed contact 188 of section 170a is connected to the movable contacts. 178 and 1800f the cam actuated switches 176 and 182.

When the main switch 162 and the motor switch 168 are closed, a circuit is completed from one of the supply lines 160 through the relay winding 172 and the switch 176 to the movable contact 180, so that when the cam 70 closes the switch 182, the relay winding 172. will be connected across. the supply lines 160. This immediately closes the contacts. 186 and 188, which completes. a holding circuitfor. the relay 170. Thus, even though the Since the two clutches are:

For simplicity, the:

normally-open contacts 180 and 184 close only momentarily as the cam 70 rotates, once the relay 170 is energized it will remain so until the cam 70 reaches the contact 178 to open the switch 176. As the switch 182 again will be open at that time, the relay holding circuit will be broken and the relay will be deenergized until the cam 70 again reaches the movable contact 180.

Closing the main power switch 162 also completes a supply circuit to a direct current power unit 190 which furnishes energizing current for the magnetic clutches. The circuit for the forward drive clutch 142 extends from the power unit 190 to the forward drive clutch winding 192 and to a fixed contact 194 on the normally-open side of a double pole section 17% of the relay 170. When the relay 170 is energized, the forward drive clutch circuit will be completed back to the power unit 190 through the movable contact 196 of the relay section 17%.

The return drive clutch circuit extends from the power unit 190 through the return drive clutch winding 198, then through a variable resistor 200 to the fixed contact 202 on the normally-closed side of the relay section 170b, and through the movable contact 196 back to the power unit. The resistor 200 is shunted by the switch 158 which is held open by the actuator 156 when the heat sealer assembly is in its rest position, but which closes when the heat sealer starts to move forward.

In the circuit as thus far described, it is seen that when the main power switch 162 and the main motor switch 168 are closed, the motor 32 will start moving material through the machine and the heat sealer will be held in its rest position by the small magnetizing current passing through the resistor 200 and the return-drive clutch winding 198. As soon as the cam 70 comes around to close the normally open switch 182, the relay will be energized, moving the contact 186 to complete the relay holding circuit and also moving the contact 196 to supply energizing current to the forward drive clutch 140. This will cause the heat sealer assembly to move forward until the cam 70 reaches the contact 178, breaking the relay circuit. Thereupon, the relay contact 196 will swing back to its starting position, completing a circuit through the return drive clutch winding 198 and the shunting switch 158. This will return the heat sealer rapidly to its starting position. Upon reaching the return limit of its travel, the heat sealer switch actuator 156 will open the switch 158, thereby putting the resistor 200 into the circuit and reducing the current through the return drive clutch winding 198, but still allowing enough current to flow through. the winding 198 to apply a small force to the return drive. clutch 142 and thereby prevent the heat sealer from rebounding.

Once the various operating parts of the machine have come up to operating speed, the switch 166 for the compressor motor 164 will be closed. The compressor Will now build up air pressure for actuating the reciprocator piston 128 (Figure 6) through the valve 130. This valve 130 is controlled by a solenoid, the winding 204 of which is connected in parallel with the relay winding 172. As long as the relay winding 172 is deenergized, the solenoid winding 204 also will be deenergized, and the valve 130 will remain in the position shown, with an open path from the actuator cylinder to the exhaust line. When the relay is energized, thereby to actuate the forward drive clutch as previously described, the valve solenoid simultaneously will move the valve to open a line 206, 208 from the compressor to the actuator cylinder. It will, of course, take a finite time for the compressed air to move the piston 128 sufficiently to bring the clamping elements 34 and 36 into engagement. Meanwhile, the clutch 142 will have had ample time to start the heat sealers in motion, so that by the time the clamp elements come together the heat sealer will be moving forward at the same speed as the moving material. On the other hand, when the cam 70 strikes the contact 178 to open the relay holding circuit, the solenoid 204 will immediately shift the valve 130 to 8 exhaust air from the cylinder, which will release the clamp elements very quickly to allow the heat sealer to be returned to its starting position.

The remaining portion of the circuit in Figure 7 is the heater section, which includes a pair of auto-transformers 208 connected across the supply lines 160 through switches 210. One of the heater elements is connected to its associated transformer 208 through a thermoswitch 212 which is located adjacent the heater, so that the heater circuit will be opened if the temperature should go above a preselected value. The other heater 110 has associated with it a thermocouple 214 and meter 216 for giving a continuous indication of tempera ture at this heater element. By observing the meter 216, the operator is enabled to select the correct operating temperature and can adjust the transformer 208 accordingly. The other transformer will be adjusted so that the thermoswitch will remain closed during normal operation of the machine, but will open the heater circuit if overheating occurs.

I claim:

1. In a bag-making machine, in combination, means for moving a continuous web of heat-scalable material in a forward direction through said machine along a predetermined path, a pair of opposed clamping elements mounted on opposite sides of said predetermined path for movement in unison backward and forward along paths parallel to a portion of said predetermined path, said elements normally being spaced apart to provide for movement of said material therebetween, first drive means connected to said elements for moving said elements forward in the direction of movement of said marterial, second drive means connected to said elements for moving said elements backward in a direction opposite to the direction of movement of said material, and first control mechanism coupled to said first and second drive means for alternately engaging said first and second drive means, a stop engaged by said clamping means at the end of backward movement, second control mechanism connected to said clamping elements, said second control mechanism being coupled to said first control mechanism and being responsive to engaging of said first drive means for bringing said elements together during forward movement of said clamping elements with said material clamped therebetween, said second drive means being partially engaged when said elements reach their limit of movement in said backward direction to apply to said elements a force tending to prevent said elements from rebounding from said stop upon their reaching said stop.

2. In a bag-making machine, in combination, driving and guiding means for moving a continuous web of heatsealable material through said machine along a predetermined path, a pair of opposed clamping elements mounted for movement in unison back and forth along paths parallel to a portion of said predetermined path, said elements normally being spaced apart to provide for movement of said material therebetween, a pair of flexible drive members connected to said elements and extending therefrom in opposite directions both of which are parallel to said portion of said predetermined path, winch means connected to said drive members and cooperable with said drive members for moving said elements back and forth, and means for bringing said elements together with said material clamped therebetween.

3. In a bag-making machine, in combination, driving and guiding means for moving a continuous web of heatsealable material through said machine along a predetermined path, a pair of clamping elements mounted for movement in unison back and forth along second and third paths coextensive with and parallel to a portion of said predetermined path, said elements normally being spaced apart with said predetermined path portion extending therebetween, a pair of flexible drive members connected to said elements and extending therefrom in opposite directions both of which are parallel to said portion of said predetermined path, Winch means connected to said drive members for moving said elements back and forth along said second and third paths, a drive motor, and a pair of magnetically actuated clutches coupling said winch means to said drive motor.

4. In a mechanism for sealing together at spaced intervals juxtaposed continuous layers of heat scalable material which are moving through said mechanism along a predetermined path, in combination, a pair of clamping elements mounted for movement in unison back and forth along second and third paths coextensive with and parallel to said predetermined path, said elements normally being spaced apart with said predetermined path extending therebetween, and drive means coupled to said elements to move said elements back and forth in unison along said second and third paths, said drive means including a pair of magnetically actuated clutches, one of said clutches being arranged to transmit driving power for moving said elements in the direction of movement of said material and the other of said clutches being arranged to transmit driving power for moving said elements in the opposite direction.

5. In a mechanism for making regularly spaced heat seals in a moving continuous web of material, in combination, a pair of clamping elements mounted for moveent back and forth along paths parallel to the path of movement of said material, drive means coupled to said elements to so move said elements back and forth in unison, said drive means including a pair of magnetically actuated clutches arranged one to transmit driving power for moving said elements in the direction of movement of said material and the other to transmit driving power for moving said elements in the opposite direction, and an actuator coupled to said elements to move said elements into and out of engagement with each other, said actuator being electrically controlled, and an electric circuit connected to said clutches and to said actuator and including switching means arranged to energize said actuator during periods of energization of said one clutch and to deenergize said actuator during periods of energization of the other of said clutches.

6. The invention defined in claim wherein said switching means includes an actuating cam coupled to be rotaited by said drive means to connect said magnetically actuated clutches alternately to said circuit.

7. In a bag-making machine, in combination, driving and guiding means for moving a continuous web of heatsealable material through said machine along a predetermined path, a pair of clamping elements mounted for movement in unison back and forth along second and third paths coextensive with and parallel to a portion of said predetermined path, said elements normally being spaced apart with said predetermined path portion extending therebetween, a pair of flexible drive members connected to said elements and extending therefrom in opposite directions both of which are parallel to said portion of said predetermined path, winch means connected to said drive members for moving said elements back and forth along said second and third paths, a drive motor, a pair of magnetically actuated clutches coupling said winch means to said drive motor, an electric circuit for supplying energizing current to said clutches, a switch connected to said circuit and to said clutches for selectively connecting said clutches to said circuit, and means including an actuating cam coupled to be rotated by said drive motor to connect said clutches to said circuit alternately through said switch.

8. In a mechanism for sealing together at spaced intervals juxtaposed continuous layers of heat scalable material which are moving through said mechanism along a predetermined path, in combination, a pair of clamping elements mounted for movement in unison back and forth along second and third paths coextensive with and parallel to said predetermined path, said elements normally being spaced apart with said predetermined path extending therebetween, drive means coupled to said elements to move said elements back and forth in unison along said second and third paths, said drive means including a pair of magnetically actuated clutches, one of said clutches being arranged to transmit driving power for moving said elements in the direction of movement of said material and the other of said clutches being arranged to transmit driving power for moving said elements in the opposite direction, and means including a pneumatically actuated piston coupled to said elements for bringing said elements into engagement during movement thereof in said direction of material movement.

9. In a mechanism for sealing together at spaced intervals juxtaposed continuous layers of heat scalable material which are moving through said mechanism along a predetermined path at a relatively high rate of speed, in combination, a support member mounted for movement back and forth along a path parallel to said first-named path, elements carried by said support member for clamping portions of said layers together and applying heat thereto to seal said portions together, a motor, drive means coupling said motor to said support member to move said support member back and forth as aforesaid, said drive means including a pair of magnetically actuated clutches, one of said clutches controlling the movement of said member in the direction of movement of said material and the other of said clutches controlling the movement of said member in the opposite direction, an electric circuit for supplying magnetizing current to said clutches, switch means connected between said clutches and said circuit for initiating and interrupting the flow of magnetizing current to said clutches, current limiting means connected between said switch means and said other clutch, a normally-open switch connected in parallel with said current limiting means for bypassing said current limiting means when said normally open switch is closed, and means carried by said support member for closing said switch when said support member reaches its limit of travel in said opposite direction.

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